1. Field of the Invention
The present invention relates to an electron beam irradiating apparatus for generating an electron beam and applying the generated electron beam to an object to be irradiated to change physical properties of the object to be irradiated.
2. Description of the Related Art
In recent years, there have been placed great expectations on an electron beam irradiating apparatus. The electron beam irradiating apparatus may be used as means for sterilizing drinking water or decomposing and removing harmful substances as well as means that contributes to our safety and health. This apparatus has recently come to play an important role especially in a semiconductor manufacturing process. This is because existing techniques face limit in increasing an integration degree of devices and improving an operational speed of the devices while following a conventional manufacturing method using a photolithography step (resist coating, pattern exposure, etching, and resist removal), and as a countermeasure against this drawback, a technique of applying an electron beam (EB) is regarded as promising (see “Nikkei MICRODEVICE” October 2002, pp. 119-128, for instance).
The conceivable use of an electron beam irradiating apparatus used in a semiconductor manufacturing process is to improve an intermediate insulating film, for example. Regarding devices having a design rule on the order of 100 nm or smaller, a wiring material has been shifted from aluminum and tungsten to copper, and a low-dielectric-constant film (also referred to as “Low-k film) has been adopted as an interlayer (interline) insulating film for increasing a speed. However, the dielectric constant of the film is reduced by using a porous film having a low film density, so a film's mechanical strength or interfacial adhesion is important. Hence, an attempt has been made to enhance the strength or adhesion through the process for irradiating the porous film with an electron beam (this process is called “EB curing process” (see “TOSHIBA Review”, Vol. 59, No. 8 (2004), pp. 17-21)).
Incidentally, a general electron beam irradiating apparatus adopts a technique of applying electrons through a window foil. In this case, the electron beam irradiating apparatus is structured as follows, for example. The electron beam irradiating apparatus is mainly composed of electron emitting means for generating and emitting an electron beam, a power supply device, and a conveying stage for positioning and moving an object to be irradiated. The electron emitting means has a vacuum chamber for protecting the following filament from damages, and a window portion for emitting the electron beam provided to the vacuum chamber. On the other hand, the conveying stage is placed outside the vacuum chamber to apply the electron beam emitted from the window portion to the object to be irradiated. The electron emitting means has a terminal for generating the electron beam provided in the vacuum chamber. The terminal has the filament as a cathode for emitting thermions, and a grid for controlling the thermions generated with the filament. The window portion has a window foil and a window structure. The window foil separates a vacuum atmosphere from a non-vacuum atmosphere in the vacuum chamber. The electron beam is emitted to the outside of the vacuum chamber through the window foil. Thus, as a material for the window foil, a high-strength titanium foil or silicon thin film is used.
However, the above conventional electron beam irradiating apparatus has the following problems to be solved.
Firstly, there is a problem in that an electron beam (thermion) is irradiated from one filament in many cases and thus, a irradiation range is narrow. To overcome this problem, the irradiation range may be widened by scanning a target with the electron beam to thereby apply the beam to a desired portion. However, in this case, electrons are applied with an energy more than required. Accordingly, a large amount of electrons pass through the object to be irradiated to cause a problem of low efficiency. Further, there are problems in that the apparatus structure has to be complicated for scanning and in that the power supply device needs to be upsized for applying the beam with the high energy, and it is also necessary to shield an X-ray resulting therefrom.
To solve the above problem of the narrow irradiation range, as shown in FIG. 6, there has been proposed an electron beam irradiating apparatus where a number of filaments and grids are provided in the terminal to ensure a wide irradiation range (see the IWASAKI ELECTRIC homepage at the Internet URL: http://www.iwasaki.co.jp/product/applied optics field/hbw system/index.html (a search was made online for this specification on Aug. 1, 2005). However, in practice, the numbers of filaments and grids that may be provided inside the terminal are limited. The electron beams (thermions) are radially emitted and thus, an amount of electron beams varies depending on an irradiation region. This leads to another problem that the physical property of the object to be irradiated which would be changed as a result of irradiation with the electron beam is not always made uniform to a sufficient degree.
Secondarily, there is a problem in that electrons pass through the titanium foil, so a high energy is necessary for emitting the electrons, with the result that the apparatus is upsized and complicated. Further, it is desirable in consideration of efficiency that the emitted electron beam is applied to the object to be irradiated with no loss, and all energy is consumed by the object to be irradiated to avoid wasteful transmission of the electron beam. However, there is a problem in that the electrons are transmitted through the titanium film, so an amount of energy necessary for electron emission is regulated during passing through the film, making it substantially impossible to adjust energy to be consumed by the object to be irradiated.
On the other hand, as an example of the conventional electron beam irradiating apparatuses, an electron beam irradiating apparatus having a window portion and devised to uniformly irradiate the object to be irradiated with an electron beam has been proposed. That is, there has been proposed an electron beam irradiating apparatus having an electron beam tube having a window portion for emitting an electron beam to the outside to process an object to be irradiated using the electron beam emitted from the electron beam tube. In this apparatus, the window portion of the electron beam tube is formed into a linear shape for linearly applying the electron beam emitted from the window portion to the object to be irradiated, and a shielding member for shielding the electron beam is provided in front of the window portion (outside the window portion) in a position facing to a part of the window portion (see JP-A-2002-341100). However, the invention disclosed in JP-A-2002-341100 has the following problem in the case of planarly applying an electron beam to a work W of a large area.
(1) An electron beam emitted from a filament 1a is absorbed by a flange 1c and a shielding member 5, resulting in an energy loss.    (2) The filament 1a cannot planarly apply an electron beam to an object to be irradiated, so plural devices (filaments 1a) are necessary, resulting in a massive system as a whole.    (3) In the case mentioned in (2) above, an irradiation amount of electron beam is reduced and its distribution becomes non-uniform due to the non-uniformity of the spaces among the plural systems.